This invention relates in general to the field of cantilever type electrical contactors, and more particularly to those that wipe (as "wipe" is defined below) across an opposing contact area while making contact therewith.
There are presently two types of contactors used to temporarily connect to miniature electronic devices for the purpose of electrical measurement: A "wiping" or cantilever contactor, and an actuated contactor. A cantilever type contactor typically has a flat spring metal arm which is canted or angled with respect to a device to be contacted. At the free end of the arm is a contact point. A contacting area of the device to be contacted is moved, actually or relatively, such that the contact point rubs, i.e. wipes, against the area and the cantilever arm is deflected slightly. Due to the spring in the arm it applies pressure on the contact area, sufficient pressure for good electrical contact. This wiping technique can use one cantilever arm and one stationary contact point, or two cantilever arms.
The wiping method, although simple and reliable, has certain drawbacks. The contacting pressure, supplied by the cantilever arm, needs to be controlled carefully. Too little pressure will result in poor electrical contact, too much pressure can damage the terminations, i.e. the contacting areas, of the device being contacted, particularly when the terminations are coated with a tin or tin/lead solder plating. Termination damage to the device is defined as any removal of the solder plating, which is typically only 100-200 microinches thick. The cantilever contact tip, being relatively stationary, wipes across the entire exposed length of the device termination, creating a relatively large mark on the termination, and greatly increasing the chances of termination damage.
Also, due to the increasing miniaturization of electronic devices, minimal clearances exist between the surface of the holding fixtures needed to hold the devices during testing and the device terminations. The result is that the cantilever tips periodically come into contact with the holding fixture. Since the cantilever tip is relatively stationary, it is abraded by the test fixture material, which is typically FR-4 glass epoxy, or a similar non-conductive material, which tends to have a moderate or high abrasive quality. The cantilever tips become rough from this contact and tend to further damage the device terminations. Also the contactor tips become dirty, either by oxidation or adherence of contaminants to the contact tips, or a combination of both. Access to the contact tips for cleaning is difficult due to the close proximity of the contact tips to the devices measured and the device holding fixture(s).
The actuated contactor technique uses moving contact tips, usually in a reciprocating motion, which are brought into contact with the devices. The contact tips are actuated for each test cycle, moved until they make contact with the device, then held stationary during the measurement of the device. After the measurement, the contacts are moved away from the device, and the device's holding plate or fixture is indexed, bringing the next device into position for the subsequent measurement. Actuated contacts can be made with very small tip sizes in order to reduce any marking of the termination ends of the tested device, unlike the wiping contact technique. Due to the high throughputs of production testing equipment, however, this actuation cycle must be done at very high speed and at rapid rates. For example, a component tester such as the Palomar Model 3300 would require 37,500 contactor actuation cycles per hour, running 150,000 parts per hour. If the components used for the actuation mechanism lasted 30,000,000 cycles, they would have to be replaced every 40 days, assuming 20 hours of machine run time per day. If the actuation time was only 10 ms in each actuation direction, the system throughput would be decreased by 10,000 parts per hour as well. Actuated contacts can also push or pull the device out of its holding plate/fixture, and the contact tips tend to be more expensive, requiring moving or flexible electrically conductive components, such as gold plated springs, or very flexible wire segments.
The contactor of this invention will allow rapid and repeated electrical connection to the terminations of many types of devices with little or no damage or markings. The electrical contactor according to this invention is a significant advance over the prior art. It eliminates the damage done to the solder plating on the terminations of devices due to the "wiping" action of the cantilever type contactors and is simpler and has a longer life than the actuated type contactor. It is particularly useful in component handlers and testers for the processing and testing of electrical circuit components, for example ceramic capacitors. (As used herein the term "component" refers to ceramic capacitors and any other electrical device having a form that allows it to be contacted by this invention.)
Other advantages and attributes of this invention will be readily discernable upon a reading of the text hereinafter.